Either way is fine. Since you are working on the hot side of the brewing process, sanitation is not a concern. So the wood dowel is fine. I use a long handled, nylon spoon with marks whittled into the plastic. One concern with the SST dip stick is that is will get hot. But that shouldn't be a big deal.
If you brew on an un-level surface, placing the dip stick in the center of the kettle will always produce an accurate volume measurement. However, if you had a sight glass on the side of the kettle, then you had better make sure the kettle is level or your volume measurement will be off.
Only bad thing about dip sticks is that the steam and heat off the wort does make you work VERY quickly!